Self servo writing file using the widest head

ABSTRACT

A self servo writing file and method for writing servo patterns in a direct access storage device are provided. First servo information is written on a data storage media at a first crash stop. The transducer heads are moved offset from the written servo information while reading the last written servo information until the detected servo signal equals a predetermined value. Then servo information is written on the data storage media responsive to the detected servo signal equal to the predetermined value. The moving and writing steps are sequentially repeated until a second crash stop is reached. A quad-burst servo amplitude pattern or phase pattern can be used for the servo information. The servo writing method is adapted easily for many different servo options. When the file uses a hybrid servo or sector servo, the other surfaces can be written by duplicating the servo bursts with a high bandwidth servo system of the file. Alternatively, the servo writing steps can be repeated for each of the other surfaces for providing head dependent pitch. Variable track pitch can be provided by selectively varying the predetermined value compared with the detected servo signal.

This application is a divisional application of Ser. No. 08/287,477filed Aug. 8, 1994 now pending, which is a continuation of Ser. No.07/896,954, filed on Jun. 11, 1992 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a direct access storage device (DASD)of the type in which a read/write transducer head is moved above astorage media for reading and writing data, and more particularly toimproved servo writing methods and apparatus for a direct access storagedevice.

2. Description of the Prior Art

Disk drive units incorporating stacked, commonly rotated rigid magneticdisks are used for storage of data in magnetic form on the disksurfaces. Transducer heads driven in a path toward and away from thedrive axis write data to the disks and read data from the disks. Data isrecorded in concentric data information tracks arrayed on the surfacesof the disks.

All DASD units must have a method to position each data head over theproper radial location to write a track and again, to position it veryclose to the same location to read the track. With the higher levelfiles using a voice coil type of actuator, a feedback mechanism must beprovided to locate and stably hold the head on a given track. Typically,track accessing and track following is provided by a magneticallywritten pattern in the DASD unit. A dedicated servo system employs onesurface of one of the disks in the DASD on which to have all thetracking and access information. A sector servo system uses smallportions of tracks between each or between several sectors on each trackof each data surface to provide the tracking and access information. Ahybrid servo system uses both to obtain advantages of each type ofservo.

Typically the servo patterns are written on the disk or disks with aspecial servo writer system. This system usually includes a lasermeasured access system to accurately position the heads. This requires aretro-reflector to be attached to the file actuator. The system alsoincludes a clock head or heads to write timing information. Each filethat is to be servo written must be firmly clamped to the servo writerto maintain accurate positioning between the two machines. The servowriter must be used in a clean area since the file must be open duringthe track writing process. This increases the cost and increases theprobability of contaminating the file.

In clamping the DASD unit to the servo writer, the natural resonances ofthe file are significantly changed. Thus while tracks written on theservo writer appear to be nearly perfect, they change when the file isremoved and the resonances change, the servo system does not follow theservo tracks perfectly, creating repeatable runout, which makes thedetermination of being on track difficult.

Examples of other known servo systems are provided by U.S. Pat. Nos.Oliver et al., 4,414,589; Penniman, 4,530,019; and Berger, 4,531,167.

Oliver et al., U.S. Pat. No. 4,414,589 discloses an embedded servo trackfollowing system and method for writing servo tracks that does notrequire a servo writer to write embedded servo data. However, a clocktrack for very accurate timing is required for providing an index ofdisc position and a measure of disc speed for writing servo data. Theclock track is written by writing a single pulse on a fixed magneticclock head, phase-lock looping to an intermediate clock track, which iswritten on a moving head, and then phase-lock looping up to the finalclock track which is written on the fixed clock track head.

Berger, U.S. Pat. No. 4,531,167 discloses a portable servo writer systemfor writing clock and servo tracks either on a dedicated disk surface orembedded servo tracks on disks of a magnetic disk drive. Servo tracksare written by providing a master disk cartridge having one fixed headand a dedicated servo surface. The master disk cartridge is installed onthe drive and the servo surface of the drive and the embedded servos arewritten using prewritten clock and index information from the fixed headof the master cartridge.

Penniman, U.S. Pat. No. 4,530,019 discloses a servo pattern including anerased gap followed by an automatic gain control (AGC) information burstfollowed by a first burst of servo control information followed by asecond burst of servo control information. The pattern is written on adisk by the disk drive unit using a mechanical index on an armatureassociated with the rotation of the disk as a primary time reference,with all other time references being based on a transition between theerased gap and the AGC burst. While the disclosed servo patterneliminates the need for a separate clock track, the mechanical index,sensors for the mechanical index, and a positioning system are requiredfor moving the read/write head to write the servo pattern.

While the prior art servo writing devices provide improvements, it isdesirable to provide an improved method for writing servo information bythe disk file and a self servo writing file where a special servo writersystem and prewritten patterns on the disks are not required and furtherthat does not require either a clock track timing reference orsubstantial different circuitry from the normally available circuitry ofthe disk file.

SUMMARY OF THE INVENTION

Important objects of the present invention are to provide an improvedself servo writing file and methods of writing servo information; toprovide improved methods of self servo writing in which variable trackwidth and head dependent pitch are enabled and optimized use of thehead/disk capability is supported; and to provide an improved self servowriting file and methods of writing servo information substantiallywithout negative effects and that overcome many disadvantages of thoseused in the past.

In brief, the objects and advantages of the present invention areachieved by a self servo writing file and method for writing servopatterns in a direct access storage device. First servo information iswritten on a data storage media at a first crash stop. The transducerheads are moved offset from the written servo information while readingthe last written servo information until the detected servo signalequals a predetermined value. Then servo information is written on thedata storage media responsive to the detected servo signal equal to thepredetermined value. The moving and writing steps are sequentiallyrepeated until a second crash stop is reached. A quad-burst servoamplitude pattern or phase pattern can be used for the servoinformation. Significant advancements are that no clock head is requiredto achieve this high bandwidth system while sector placement ismaintained in a repeatable radial spoke like arrangement.

In accordance with the invention, the servo writing method is adaptedeasily for many different servo options. When the file uses a hybridservo or sector servo, the other surfaces can be written by duplicatingthe servo bursts or any servo pattern with a high bandwidth servosystem. Alternatively, the servo writing steps can be repeated for eachof the other surfaces providing head dependent pitch. Variable trackpitch can be provided by selectively varying the predetermined valuecompared with the detected servo signal.

BRIEF DESCRIPTION OF THE DRAWING

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the embodiment of the invention illustrated in thedrawing, wherein:

FIG. 1 is a schematic and simplified vertical sectional view of a rigidmagnetic disk drive unit embodying the present invention;

FIG. 2 is a top plan view of the structure shown in FIG. 1;

FIG. 3 is a flow chart illustrating sequential operations of the selfservo writing file of the invention;

FIGS. 4A, 4B, 4C and 4D are flow charts illustrating alternativesequential operations of the self servo writing file of the invention;

FIG. 5 illustrates a quad burst servo pattern for the self servo writingfile of the invention;

FIG. 6 illustrates servo signals for the self servo writing file of theinvention;

FIG. 7 is a flow chart illustrating alternative sequential operations ofa self servo writing file of the invention; and

FIG. 8 is a flow chart illustrating sequential operations foridentifying an offset table and rewriting calibration patterns in themethod of the self servo writing file shown in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 there is shown a partly schematic block diagram of parts of adata storage disk file 10 including a rigid magnetic disk drive unitgenerally designated as 12 and a control unit generally designated as14. While a magnetic disk drive unit is illustrated, it should beunderstood that other mechanically moving memory configurations may beused. Unit 12 is illustrated in simplified form sufficient for anunderstanding of the present invention because the utility of thepresent invention is not limited to the details of a particular driveunit construction. After data storage disk file 10 is completelyassembled, servo information used to write and read data is writtenusing the disk file 10. The need for prerecorded servo patterns oftenwritten with a servo writer system is eliminated.

Referring now to FIGS. 1 and 2 of the drawing, disk drive unit 12includes a stack 16 of disks 18 having at least one magnetic surface 20.The disks 18 are mounted in parallel for simultaneous rotation on and byan integrated spindle and motor assembly 26. Data information on eachdisk 18 are read and/or written to by a corresponding transducer head 28movable across the disk surface 20. In a disk drive using a dedicated orhybrid servo, one of the disk surfaces 20' stores servo information usedto locate information and data on the other disk surfaces 20.

Transducer heads 28 are mounted on flexure springs 30 carried by arms 32ganged together for simultaneous pivotal movement about a supportspindle 34. One of the arms 32 includes an extension 36 driven in apivotal motion by a head drive motor 38. Although several drivearrangements are commonly used, the motor 38 can include a voice coilmotor 40 cooperating with a magnet and core assembly (not seen)operatively controlled for moving the transducer heads 28 in synchronismin a radial direction in order to position the heads in registrationwith data information tracks or data cylinders 42 to be followed andaccess particular data sectors 44. Although a rotary actuator is shown,it should be understood that a disk drive with a linear actuator can beused. Data storage disk file 10 is a modular unit including a housing46. The various components of the disk file 10 are controlled inoperation by signals generated by control unit 14 such as motor controlsignals on line 26A and position control signals on line 38A.

Numerous data information tracks 42 are arrayed in a concentric patternin the magnetic medium of each disk surface 20 of data disks 18. A datacylinder includes a set of corresponding data information tracks 42 forthe data surfaces 20 in the data storage disk file 10. Data informationtracks 42 include a plurality of segments or data sectors 44 each forcontaining a predefined size of individual groups of data records whichare saved for later retrieval and updates. The data information tracks42 are disposed at predetermined positions relative to servoinformation, such as a servo reference index. In FIG. 2 one sector 44 isillustrated as SECTOR O with a fixed index or mark INDEX for properlylocating the first data sector. The location of each next sector 44 isidentified by a sector identification (SID) pulse read by transducerheads 28 from surfaces 20, 20'.

In FIG. 3, there is shown a flow chart illustrating the self-servowriting accomplished by a boot-strap method of the invention beginningat a block 300. Sequential operations begin with the file started withthe actuator at the inner diameter (ID) stop as indicated at a block302. File 10 is spun up with the actuator latched against the inner (ID)crash stop as indicated at the block 302. Disks 18 in the DASD 10preferably will have no signal present on the surfaces 20 and 20'.Alternatively, the disk surfaces 20 and 20' will be erased in the file,however this is more difficult.

First the latch is released, and a small current is applied to move theactuator towards the outer crash stop. The actuator bounces to a stop atthe outer (OD) crash stop as indicated at a block 304.

A quad-burst servo pattern as disclosed in "QUAD BURST SERVO NEEDING NOSYNC ID AND HAVING ADDED INFORMATION", IBM Technical Disclosure BulletinVol. 33, No. 3B, August 1990 advantageously is used. As illustrated inFIG. 5, the quad-burst servo pattern consists of four different baseamplitude patterns with the same fundamental frequency. Each of the fourpattern types are written in the corresponding offtrack positionsseparated in time designated by A, C, B, and D. Each burst has thecapability of providing self identification. Accurate timing ofinformation between bursts is not required for reading the servopattern. FIG. 6 illustrates the primary position error signal (PES) or Psignal and the quadrature PES or Q signal used for writing the servopattern. Alternatively, a more standard approach of an ID field and theservo burst could be used for each burst of the amplitude pattern, suchthat reading the pattern never requires the timing of informationbetween tracks. Note that quad-burst patterns have at least one trackwidth of erased data beside each burst so that no other signal is pickedup even if the head is significantly offset from a given pattern.

Each head 28 is used to burst write a servo pattern A at the OD crashstop as indicated at a block 306. The amplitude of each head is measuredand saved as indicated at a block 308. As indicated at a decision block310 offset measurements are made. The offset available by using thereduced track amplitude is less than the physical track width. Since thetrack width of a head is about 3/4 of the desired pitch, an offset of1/2 of the track pitch can be used; however, it should be understoodthat another value may be used if desired. One head is selectedarbitrarily indicated as head 1 in a block 312 to servo away from thestop a selected offset, for example, about 1/2 track. Head 1 is moveduntil an empirically predetermined ratio S of amplitude at 1/2 trackoffset to amplitude on track is detected.

Offset amplitudes of all the heads are measured and then compared to theoriginal amplitudes at block 310. A maximum ratio head having thelargest fraction or maximum ratio corresponding to the widest head onthe actuator is identified and saved as indicated at a block 314. Thenthe written pitch is referenced to this maximum ratio head to allowenough room to prevent too much squeeze. This can be used to allow datato be written at larger radii reducing linear density and improvingquality or by allowing higher capacity offerings from the same basemodel file 10.

Other information about the track misregistration (TMR) distribution ondifferent heads, or from a squeeze test can be used to influence theselection of the nominal pitch for the file.

Once the selected pitch is determined, a reference head is selected tobe the dominant servo head for writing the file. The reference head canbe the widest head saved at the block 314. Alternatively, when adedicated servo surface or a hybrid servo is to be written, the servohead is selected as the reference head. Other basis for the referencehead selection could be the head with the highest signal orsignal-to-noise estimate, or a position in the disk stack that is knownto have the least TMR.

Then the maximum ratio head is moved until the measured ratio equals theempirically predetermined ratio S as indicated at a block 316. Then theamplitude for the selected reference head is measured and compared withthe original amplitude and a ratio T is saved as indicated at block 318.

Next the OD stop outer track is written with the burst pattern of thetype defined as A as shown in FIG. 4, if required, as indicated atblocks 320 and 322. On track amplitudes are measured and saved asindicated at a block 324. When the original amplitude track written atblock 306 is adequate, it can be used; otherwise, a new pattern A iswritten at the block 322 with the erase left on between the bursts. Whenthe start to stop timing or spacing of the first to last burst isinadequate, the burst pattern A is rewritten with erase on betweenbursts until adequate closure is obtained.

A low bandwidth servo system is used so that any written track will notcontain any significant amount of repeatable runout, except for smallnoise deviations, and the head will therefore follow its natural course.The low bandwidth servo requirement prevents the build-up of repeatablerunout, that would result if a high bandwidth system were used. Thestart of write is obtained from a motor pulse for index. The burstpatterns are written with bursts phase lock loop (PLL) synchronized tomotor revolution.

Next it is determined if the reference head is at the ID crash stop asindicated at a decision block 326. If not, the head actuator is movedofftrack by 1/2 of the track pitch identified by a measured ratio T forthe reference head as indicated at a block 328. Then the buffer patternis incremented as indicated at a block 330 so that following type Abursts, type C bursts are written at block 322 starting a given timeafter the start of each type A burst. The current is turned off betweenthe bursts to avoid erasing edges of the previously written bursts.

The servo system measures the average ontrack amplitude of the type Cbursts and establishes the threshold level T as the fraction of themeasured average amplitude, to be used as the servo reference. The servosystem is then switched to the C signal and the head accessed until theamplitude equals the calculated threshold.

Next the sequential steps are repeated and type B bursts are written,timing off the type C bursts. Then the type D bursts are written, timingoff the type B bursts. The head is now approximately aligned with thetype A bursts written two customer tracks back. The sequential steps arerepeated until the reference head reaches the ID crash stop identifiedat block 326.

To maintain uniform burst spacing, an average timing value betweenprevious track bursts is established. Uniform burst spacing can beaccomplished using a given number of cycles of a crystal clock. Theclock is high frequency so there are hundreds of cycles counted toestablish the nominal burst spacing. The count of the reference clockcounter at the time of the previous burst is compared to the expectedcount and correction is applied for the average error over multiplebursts. When the error indicates the bursts are occurring later on theaverage than the expected, the burst spacing count is corrected to delaythe calculated expected positions. In this way, an averaging of theburst spacings is performed and bursts are written much more uniformlyso that the variability of the burst spacing does not significantlyaccumulate.

This action provides a uniform spacing between bursts. However, therecan still be a small timing offset between tracks that can accumulateand can produce a slow change in the circumferential position of thebursts versus radius. The average circumferential position of the burstscan be compared to the motor drive timings. Any error is averaged over alarger period and can also be used to change the number of crystal clockcounts per burst. Using this feedback, significant creep of bursts inthe circumferential direction versus radius is prevented.

After one whole surface is written, the other surfaces are written forsector servo or hybrid servo files, by switching to the high bandwidthservo using the difference between two bands for the PES, andduplicating the servo bursts onto the other surfaces. For example, withthe head centered between the type A and type B bursts, the type Cbursts are written on all the other surfaces, multiplexing the read ofthe A and B signals with the write of the C burst between. In a similarmanner, all the other bursts can be duplicated, except the last type oneach end of the data band. These are not needed but could be written ifdesired by moving against the crash stops.

Alternatively the above sequential self-servo writing steps can beperformed for separately writing each surface for providing headdependent pitch. In this case, each surface has a different trackdensity, according to the track width of the next head. The use of apitch to match each head allows more optimum use of each head'scapability. Then each head defines the servo and the sequential steps ofselecting the widest head for the maximum ratio head are eliminated.

The averaging of burst positions to create a circumferential or angularposition reference allows the writing of servo tracks without requiringthe use of a clock head. Eliminating use of the clock head is asignificant advancement over known arrangements. Typically a clock headhas been used to overcome the circumferential timing synchronizingproblem on the surface of the disk. Using the motor drive or clockfrequency multiples allows synchronization with the disk surfaceeliminating the need for a clock head.

Even though a clock head is not required, high bandwidth and high burstdensity can be achieved. The use of the file clock and PLL synchronizedmotor drive commands allows accurate placement of the servo burstscircumferentially around the track. The accurate burst placement allowsa very high density of bursts to be written. The high burst densitydirectly contributes to increasing the servo position sample rate whichincreases the available servo bandwidth capability. Hence the bandwidthis not limited by the number of motor poles or electrical drive cycles.

The technique for maintaining burst position synchronization with theangular displacement on the disk is key for providing a stable index andan orderly spoke like sector arrangement on the disk surface. Thisenhances the control over sector positioning on the disk surface andallows optimal arrangement of the sectors for maximum throughput.

It should be understood that for a track density selected either for allsurfaces in common, or for each surface separately, it is not necessaryto maintain a constant track density across the radial band. The pitchcan be selectively varied by using an algorithm to selectively vary thefraction of full amplitude that is detected for moving the actuator inthe servo-writing offtrack positioning at block 328.

Referring now to FIGS. 4A, 4B, 4C and 4D, alternative sequentialoperations of the self servo writing file 10 are illustrated forimplementing the burst writing step of block 322 of FIG. 3. In FIG. 4A,the sequential operations begin at a block 400 for a first case withbursts PLL synchronized to motor revolution. Counts of burst writestarts and stops are initialized at a block 402 and a count value for afull revolution is set at a block 404. Next at a decision block 406, amodulo count is compared with a burst write start. When equal, thebuffer pattern write is started as indicated at a block 408. Otherwiseor after starting the buffer pattern write, then at a decision block 410a modulo count is compared with a burst write stop. When equal, thebuffer pattern write is stopped as indicated at a block 412. Thesequential operations are repeated returning to the decision block 406,until a completed revolution is identified at a decision block 414. Thenthe sequential operations continue to block 324 in FIG. 3.

In FIG. 4B, the sequential operations begin at a block 418 for a secondcase with nonsynchronized triggered burst writes that is subject togreater motor speed variation error. First it is determined if the headis forced against the OD stop at a decision block 420. If yes, then aninitial burst track write is performed until closure is achieved asindicated at a block 422 and then the sequential operations continue toblock 324 in FIG. 3. Otherwise, a new burst is written by first asindicated at a block 424 to lock the PLL on to previous track bursts,then to trigger the counter by threshold detection of the start of theprevious track burst at a block 426. When a count equal to the burststart separation count is identified at a decision block 428, then thenew burst is written at a block 430. The sequential operations arerepeated returning to block 426, until the last burst on the track hasbeen written identified at a decision block 432. Then the sequentialoperations continue to block 324 in FIG. 3. In FIG. 4C, the sequentialoperations begin at a block 436 for a third case with nonsynchronizedaveraged triggered burst writes that reduces average burst start error.First it is determined if the head is forced against the OD stop at adecision block 438. If yes, then an initial burst track write isperformed until closure is achieved as indicated at a block 440 and thenthe sequential operations continue to block 324 in FIG. 3. Otherwise, anew burst is written by first as indicated at a block 442 to lock thePLL on to previous track bursts, then to trigger the counter start byaveraging burst start detected threshold timings at a block 444. When acount equal to the burst start separation count is identified at adecision block 446, then the new burst is written at a block 448. Thesequential operations are repeated returning to block 442, until thelast burst on the track has been written identified at a decision block450. Then the sequential operations continue to block 324 in FIG. 3. InFIG. 4D, the sequential operations begin at a block 454 for a fourthcase with nonsynchronized averaged triggered burst writes with indexcorrection that reduces average burst start error and corrects for indexdrift around the revolution. First it is determined if the head isforced against the OD stop at a decision block 456. If yes, then aninitial burst track write is performed until closure is achieved asindicated at a block 458 and then the sequential operations continue toblock 324 in FIG. 3. Otherwise, a new burst is written by first asindicated at a block 459 to lock the PLL on to previous track bursts,then to trigger the counter start by averaging burst start detectedthreshold timings and track average time at a block 444. When a countequal to the burst start separation count is identified at a decisionblock 462, then the new burst is written at a block 464. The next stepis to update average track time correction by the difference to thepresent driver or PLL motor lock time as indicated at a block 466. Thenthe sequential operations are repeated returning to block 460, until thelast burst on the track has been written identified at a decision block468. Then the sequential operations continue to block 324 in FIG. 3.

In FIG. 7, there is shown a flow chart illustrating an alternativeself-servo writing method of the invention beginning at a block 700.First master disk surface is erased as indicated at a block 702 in thealternative self-servo writing method. Erasing can be accomplished byturning on the head write current with a DC data signal while slowlymoving the head across the master disk surface. To minimize the numberof missed spots that occur if the head moves too fast during erasing,repeated passes over the disk can be made. By controlling the velocitysuch that the head moves less than one head width per disk revolution,erasing can be provided with a single pass. Constant velocity moves canbe accomplished by back EMF sensing of the actuator motor to determineits velocity. Also when a large percentage of the disk surface iserased, for example, such as more than 90%, then this self-servo writingmethod can be performed.

Next a clock track is written at one of the crash stops, such as the IDcrash stop as indicated at a block 704. A stable clock source, such as acrystal clock, is used to write a required number of clocks on the diskusing a single head at the block 704. After a clock track is written,the number of clocks actually written for one revolution is countedusing an index mark encoded in the clock data to determine when to startand stop counting. When the disk is rotating at the proper speed, therequired number of clocks (N) are written on the disk and clock writingis complete. Otherwise, repeated clock writing trials and tests are madeuntil exactly N clocks are written to the disk. Since the clock sourceis fixed in frequency, only the disk speed is varied for each clockwriting trial until the correct number of N clocks are written.

Bursts of servo information are written over the clock track,periodically around the track as indicated at a block 706. Then eachclock burst between the servo information bursts are divided into twohalves, naming the first half the odd clock burst and the second halfthe even clock burst as indicated at a block 708. Next as indicated at ablock 710, the head is moved using the odd clock track signal amplitudeas a servo signal, until the amplitude drops to a predetermined valueT1, for example, such as 60% as indicated in a decision block 712. Theneven clock burst and servo information are written for this headposition while servoing and synchronizing the system timing off the oddclock burst on the previous track as indicated at a block 714. At block714, the servo information is written aligned in time with the servoburst on the previous track.

Next as indicated at a block 716, the head is moved using the even clocktrack signal amplitude as a servo signal until the amplitude drops tothe predetermined value T1, as indicated in a decision block 718. Thenodd clock burst is written for this head position while servoing andsynchronizing the system timing off the even clock burst on the previoustrack as indicated at a block 720. Then the sequential steps arerepeated returning to block 710 until the head is moved all the wayacross the disk to the OD crash stop as indicated at a decision block722 to complete the servo writing process. Then a calibration pattern iswritten between each odd and even clock bursts where no servo patternhad been written previously over the disk surface. The calibrationpatterns are written using the servo patterns for positioning the headas indicated at a block 724. After writing the entire surface with thecalibration servo patterns at block 724, then each calibration servopattern is read back as indicated at a block 726 in order to determineany offsets, for example due to head geometric effects and the coarsepositioning used in blocks 710 and 716, as indicated at a block 726.Identified offsets are stored in an offset table as indicated at a block728. Then moving to a next track, calibration patterns are repeatedlyread at block 726 and stored in the offset table at the block 728 untilall tracks have been read as identified at a decision block 730. Thenthe calibration patterns are rewritten as indicated at a block 732,using the stored offset table for position correction adjustments. Therewritten calibration patterns are evenly spaced at the proper trackspacing and then serve as the master pattern for the disk file. Theoriginally written servo patterns are no longer needed and can beoverwritten. For sector servo or hybrid servo files, the servoinformation and clock information between servo bursts can be written onthe other surfaces.

Referring now to FIG. 8, there is shown a flow chart illustratingsequential steps for read back of the calibration patterns and rewritingthe calibration patterns at blocks 726-732 of FIG. 7. The sequentialoperations begin at a first track as indicated at a block 802. Thenservo information or servo pattern is read as indicated at a block 804to determine an average for the track. Next the calibration patterns forthat track are read as indicated at a block 806 to determine an averagecalibration value. The difference between the calibration and servopattern averages is recorded as indicated at a block 808. Unless thelast track is identified at a decision block 810, then the sequentialoperation continues with a next adjacent track as indicated at a block812. After all the servo and calibration patterns from the last trackhave been read and the differences recorded, then an average value ofall recorded differences is calculated as indicated at a block 814. Thenthe identified average value is subtracted from each recorded differenceto store the offset table as indicated at a block 816. Then thecalibration patterns are rewritten, using the stored offset table forposition correction adjustments, as indicated at a block 818. Thesequential steps at blocks 802-818, inclusive, then can be repeated toachieve the master pattern for the disk file.

While the invention has been described with reference to details of theillustrated embodiment, these details are not intended to limit thescope of the invention as defined in the appended claims.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A method for writing servo patterns in a directaccess storage device including a plurality of data storage mediamounted for simultaneous rotation about an axis and an actuator formoving each of a plurality of transducer means relative to an associateddata storage media for reading and writing data to the associated datastorage media, said method comprising the steps of:utilizing each ofsaid plurality of transducer means and writing a data pattern torespective data storage media; identifying one of said plurality oftransducer means having a widest head; and saving said identifiedtransducer means having said widest head as a reference head for writingservo patterns to said data storage media.
 2. A method for writing servopatterns in a direct access storage device as recited in claim 1 whereinsaid step of identifying one of said plurality of transducer meanshaving a widest head includes the steps of: selecting one of saidplurality of transducer means and moving said selected one of saidplurality of transducer means by a selected offset.
 3. A method forwriting servo patterns in a direct access storage device as recited inclaim 2 includes the steps of measuring and saving an original amplitudeof each of said plurality of transducer means and measuring and savingan offset amplitude of each of said plurality of transducer means.
 4. Amethod for writing servo patterns in a direct access storage device asrecited in claim 3 includes the steps of comparing each said offsetamplitude with said original amplitude of each of said plurality oftransducer means.
 5. A method for writing servo patterns in a directaccess storage device as recited in claim 4 includes the steps ofidentifying one of said plurality of transducer means having a maximumratio to identify said one of said plurality of transducer means havinga widest head.
 6. A method for writing servo patterns in a direct accessstorage device as recited in claim 1 wherein said step of saving saididentified transducer means having said widest head for referencing thewriting servo patterns to said data storage media includes the step ofreferencing a written pitch of the written servo patterns to said widesthead.
 7. A method for writing servo patterns in a direct access storagedevice as recited in claim 1 wherein said step of saving said identifiedtransducer means having said widest head for referencing the writingservo patterns to said data storage media includes the step of selectingsaid identified transducer means having said widest head as a referencehead for writing servo patterns to said data storage media.
 8. A selfservo writing file comprising:a plurality of data storage media mountedfor simultaneous rotation about an axis; an actuator for moving each ofa plurality of transducer means relative to an associated data storagemedia for reading and writing data to the associated data storage media,means for writing a data pattern to respective data storage mediautilizing each of said plurality of transducer means; means foridentifying one of said plurality of transducer means having a widesthead; and means for saving said identified transducer means having saidwidest head as a reference head for writing servo patterns to said datastorage media.
 9. A self servo writing file as recited in claim 8further includes a housing containing said plurality of data storagemedia and said plurality of transducer means.
 10. A self servo writingfile as recited in claim 9 wherein said means for saving said identifiedtransducer means having said widest head for referencing the writingservo patterns to said data storage media includes means for referencinga written pitch of the written servo patterns to said widest head.
 11. Aself servo writing file as recited in claim 10 wherein said means forsaving said identified transducer means having said widest head forreferencing the writing servo patterns to said data storage mediaincludes means for selecting said identified transducer means havingsaid widest head as a reference head for writing servo patterns to saiddata storage media.
 12. A self servo writing file as recited in claim 8wherein said means for identifying said one of said plurality oftransducer means having a widest head includes means for measuring andsaving an original amplitude of each of said plurality of transducermeans and means for moving and for measuring and saving an offsetamplitude of each of said plurality of transducer means.
 13. A selfservo writing file as recited in claim 12 further includes means foridentifying one of said plurality of transducer means having a maximumratio of said original amplitude and said offset amplitude to identifysaid one of said plurality of transducer means having a widest head.